Glucagon is produced in humans by the pancreas. Glucagon binds to specific receptors on liver cells and increases the release of glucose in the blood stream. Thus, it is used in the treatment of diabetes as a rescue medication when the blood sugar level drops too low.
Glucagon is a short peptide having 29 amino acids and a molecular weight of 3,483 kilodaltons (kDa). The sequence of amino acid in glucagon is:
(SEQ ID NO: 1)His Ser Gln Gly Thr Phe Thr Ser Asp Tyr Ser Lys1                5                  10 Tyr Leu Asp Ser Arg Arg Ala Gln Asp Phe Val Gln        15                  20  21 Trp Leu Met Asn Thr25              29
Glucagon has a highly helical conformation in the crystalline state, but forms a random coil in dilute solution with about 15% alpha helix at the C-terminus. At higher concentrations it generally precipitates and forms fibrils. Glucagon readily dissolved in aqueous solution at pH below 3 or above 9, but precipitates readily at pH between 4 and 8. Liquid formulations of glucagon are highly unstable, and undergo hydrolysis and deamidation at several positions (amino acid at position 3, 9, 15, 20, 21, and 24) and thus pharmaceutical preparations are generally provided in dual containers: powders of glucagon in one side and a liquid diluent in another. A solution of glucagon is then prepared just prior to use. Procedures generally undertaken to mitigate the instability of glucagon in liquid formulations include the use of solid dispersions, aprotic solvents, surfactants, processes conducted at low temperature, and packaging in dried form.
Dilute formulations have been prepared that are stable for up to 6 days and are useful for delivery with a pump (US2011/0097386). The concentration of glucagon in these formulations is between 0.8 mg/mL to 5 mg/mL and the pH is between 4 and 7. Stabilizing agents are a combination of both low concentrations of a surfactant such as 1 mg/ml lyso-myristoyl phosphatidylcholine (LMPC) and high concentrations of saccharide such as 45 mg/mL of glucose.
Additionally, Applicant describes herein a highly concentrated liquid glucagon formulation that is stable for at least 4 days with the utilization of Sodium Carboxymethyl Cellulose (NaCMC) to prevent fibril and/or gelation of glucagon.